Package delivery companies pick up millions of packages daily from thousands of locations over a large geographical area and transport them, primarily by truck and airplane, to a correspondingly large number of scattered destinations. To meet a rigorous schedule and provide accurate deliveries, a package delivery company must use automated transfer systems to match packages arriving at its sorting hubs with proper outgoing transport headed for the packages' destinations. Because deliveries are time sensitive, the sorting equipment must be fast, yet provide accurate and gentle handling of packages.
For these reasons, automatic package sorting systems are rapidly replacing manual sorting stations in package delivery company facilities. Various types of sorting systems have been developed for different needs. To be cost effective, an automatic package sorting system must have a minimum number of moving parts, be easily repairable with minimum downtime, and occupy a minimum amount of space in a sorting "hub" facility.
One type of automatic package sorting system utilizes a tilted conveyor on which parcels are held by a stationary wall in which gates are defined at discharge locations. Systems of this kind are shown in U.S. Pat. Nos. 3,880,751; 3,918,572; and 3,913,730. In such prior systems, a parcel typically slides laterally from the conveyor under the force of gravity, through an opening in the wall formed when a gate is lowered. The conveyor itself is made sufficiently wide to accommodate the full width of the largest expected parcel. Such systems can be operated at high conveyor speeds when used to sort small parcels that pass quickly through the gates. However, larger, heavier parcels slide more slowly from the conveyor, and therefore require slower operation and more spacing between parcels.
U.S. Pat. Nos. 3,880,751 describes a tilted conveyor sorter in which the gates in the guide wall each have a wedge-shaped partial closure wall portion in the trailing portion of the gate. The momentum of the parcels is said to carry them through the opening in the guide wall, and the inclined wedge is intended to accentuate the turning action of the parcels. This action is said to allow closing of the gate to begin before the parcel has cleared the opening, which in turn allows closer spacing of parcels. However, the turning action of the wedge can cause the parcels to tumble, as noted in U.S. Pat. No. 3,918,572.
In the case of larger parcels, the momentum of the parcel at high speed cannot be controlled and directed so easily, and a rapid closing of the gate could result in the parcel not making it through the opening in time. Thus, there is a need for an apparatus capable of isolating large parcels from the driving force of the conveyor, while at the same time discharging the parcel quickly, and closing the gate before the parcel passes completely through the barrier to minimize spacing between parcels.